我如何计算值（重复除外）？

Question

如何计算列中的值（重复项除外）。我尝试这个代码，但我没有。谢谢你的帮助。 （对不起，我的英文不好）

long net = DatabaseUtils.longForQuery(db, "select date, count(*) from  mytable GROUP BY date", null);
nettext.setText(String.valueOf(net));     

For example:
+----+------------+
| id | date       |
+----+------------+
|  1 | 2006-10-08 |
|  2 | 2006-10-08 |
|  3 | 2006-10-09 |
+----+------------+

There is two different date (2006-10-08 and 2006-10-09)
Result must be = 2

Answer 1

这应该有效：

long net = DatabaseUtils.longForQuery(db, "select count(DISTINCT date) from  mytable GROUP BY date", null);

Answer 2

我找到了解决方案。谢谢m.aibin。

long net = DatabaseUtils.longForQuery(db, "select count(DISTINCT date) from  mytable", null);